Neutron diffraction studies are proposed to describe the structure and dynamics of filamentous bacteriophages fd and Pf1. Solid state NMR studies of both C-D and N-D sites will be used further to characterize these virions. These experiments will contribute to an understanding of the protein-DNA and protein-protein interactions in the intact virions and to the characterization of the conformational switching of virion components during the phage life cycle. The studies will be closely coordinated with complementary experiments using X-ray diffraction and solid state NMR. This close coordination among methods will allow an optimum use of the required resources and provide a broad perspective from which to interpret experimental results. Neutron diffraction is unique in its ability to locate deuterium in a structure (and thus hydrogen atoms or water molecules). Because of this it can provide structural information not obtainable by other techniques. H2O/D2O exchange will be used to study the hydration of the DNA and the DNA-protein interactions in the phage particles. H/D exchange at elevated temperatures will provide insight into the structural changes which take place at 60-65 C in these virions. Diffraction from phage specifically labeled with deuterated amino acids will be used to determine the positions of the residues in the virus particle and to constrain structural models for the virus coat protein. X-ray and neutron diffraction from coat protein in lipid bilayers will contribute to an understanding of the membrane mediated assembly process of the phage particles. Combined with X-ray diffraction and NMR studies, these results will provide a detailed characterization of the structure and assembly of the filamentous bacteriophages. The development of this coordinated approach to the study of macromolecular assemblies holds great promise for the study of the molecular architecture and dynamics of many subcellular organelles.